1. Field of the Invention
The present invention relates to a lamination-type resistance element and more particularly to a lamination-type resistance element in which internal electrodes are disposed inside a laminated sinter so as to enable fine adjustment of a resistance value.
2. Description of the Related Art
To date, resistance elements such as PTC thermistors and NTC thermistors have been used for temperature compensation and temperature detection. Among such resistance elements, there is a lamination-type resistance element that can be mounted on a printed circuit board, etc. Hereinafter, examples of related lamination-type resistance elements are described.
FIG. 7 is a sectional view showing a first related example wherein the resistance element is an NTC thermistor.
In a lamination-type thermistor 1 shown in FIG. 7, first internal electrodes 4a and 4b and second internal electrodes 5a and 5b are provided inside a laminated sinter 3 in which a plurality of thermistor layers 2 are integrally sintered. External electrodes 7 and 8 are provided on the outer surface and more specifically on both end portions of the laminated sinter 3.
One end portion of the first internal electrode 4a and one end portion of the second internal electrode 5a face each other on the same planar surface with a gap 6a therebetween. The other end portion of the first internal electrode 4a is electrically connected to the external electrode 7 and the other end portion of the second internal electrode 4b is electrically connected to the external electrode 8.
Furthermore, one end portion of the first internal electrode 4b and one end portion of the second internal electrode 5b face each other on the same planar surface with a gap 6b therebetween. The other end portion of the first internal electrode 4b is electrically connected to the external electrode 7 and the other end portion of the second internal electrode 5b is electrically connected to the external electrode 8.
The gaps 6a and the gaps 6b are alternately disposed along the lamination direction of the plurality of thermistor layers 2 inside the laminated sinter 3. Furthermore, the gaps 6a and the gaps 6b are arranged at different locations in the direction that is substantially perpendicular to the lamination direction of the laminated sinter 3.
FIG. 8 is a sectional view showing a second related example and, in the same way as in FIG. 7, the resistance element is an NTC thermistor.
In a lamination-type NTC thermistor 11 shown in FIG. 8, first internal electrodes 14a and second internal electrodes 14b are provided inside a laminated sinter 13 in which a plurality of thermistor layers 12 are integrally sintered. Furthermore, internal electrodes 16 are arranged so as to face the first internal electrodes 14a and second internal electrodes 14b through a thermistor layer 12. External electrodes 17 and 18 are provided on the outer surface of the laminated sinter 12 and more specifically on both end portions.
One end portion of the first internal electrode 14a and one end portion of the second internal electrode 14b are arranged so as to face each other on the same plane with a gap 15 therebetween. The other end portion of the first internal electrode 14a is electrically connected to the external electrode 17 and the other end portion of the second internal electrode 14b is electrically connected to the external electrode 18.
The internal electrode 16 is a no-connection-type internal electrode, both end portions of which are not extended out to the outer surface of the laminated sinter 13 and which are not connected to the external electrodes 17 and 18.
The resistance value of the first related lamination-type resistance element is determined by the size of the gap 6a between the first internal electrode 4a and the second internal electrode 5a, the size of the gap 6b between the first internal electrode 4b and the second internal electrode 5b, and the overlapping area between the first internal electrode 4a and the second internal electrode 5b and the space therebetween.
Furthermore, the resistance value of the second related lamination-type resistance element is determined by the size of the gap 15 between the first internal electrode 14a and the second internal electrode 14b, the overlapping area between the first internal electrode 14a and the no-connection-type internal electrode 16 and the space therebetween, and the overlapping area between the second internal electrode 14b and the no-connection-type internal electrode 16 and the space therebetween.
In Japanese Unexamined Patent Application Publication No. 2000-124008, a third related lamination-type resistance element is disclosed. In a resistance element disclosed in Japanese Unexamined Patent Application Publication No. 2000-124008, inside a negative characteristic thermistor element, first and second internal electrodes are disposed so as to lie on top of one another with a thermistor element layer therebetween, the internal electrode is extended out to one end of the negative characteristic thermistor element, and the other internal electrode is extended out to the other end. Then, the first and second external electrodes are arranged at both ends of the thermistor element. Furthermore, a resistor layer made of a resistive material that is different from the material defining the thermistor element is laminated on the thermistor element. Then, a pair of internal electrodes, one end of each facing one end of the other with a gap therebetween on the same plane, are provided inside of the resistor layer. One of the internal electrodes is electrically connected to the first external electrode and the other is electrically connected to the second external electrode.
Here, the resistance value can be set by adjustment of not only material characteristics and the shape of the above-described resistor layer, but also the pattern of a pair of electrodes inside the resonator layer, and thus, the freedom of setting the resistance value can be increased.
Furthermore, in Japanese Unexamined Utility Model Registration Application Publication No. 6-34201, an NTC thermistor as a lamination-type resistance element according to a fourth example is disclosed. That is, an NTC thermistor in which a plurality of pairs of internal electrodes, the inner end of one of the pair facing the inner end of the other with a gap therebetween on the same plane, are provided inside a lamination-type resistor. Here, in each pair of internal electrodes, one internal electrode is electrically connected to a first external electrode provided on one end surface of the resistor and the other internal electrode is electrically connected to a second external electrode provided on the other end surface of the resistor. Then, when seen from a direction perpendicular to the upper surface of the resistor, in each of the plurality of pairs, the one internal electrode and the other internal electrode are disposed so as not to lie on top of one another. In this NTC thermistor, since the resistance value is determined by the size of a gap between a pair of internal electrodes disposed on the same plane, it is possible to reduce variations of the resistance value.
When the resistance value is adjusted in the first and second lamination-type resistance elements, the number of laminations of each internal electrode is increased or reduced. However, in the case of adjustment of the resistance value, in the first related example, since the number of internal electrodes 4a, 4b, 5a, and 5b facing each other through a thermistor layer 2 is increased or reduced, the range of change of the resistance value is wide and fine adjustment of the resistance value is difficult. In the second related example, the number of units made of internal electrodes 14a and 14b and internal electrodes 16 facing each other through a thermistor 12 is increased or decreased. Accordingly, the range of change of the resistance value is also wide and fine adjustment of the resistance value is difficult.
On the other hand, in the lamination-type resistance element of the third related example, since the resistor layer is made using a material different from a negative characteristic thermistor element, the manufacturing process becomes complicated and, as a matter of course, the cost increases. Furthermore, since the thickness of the resistor layer is required to be sufficiently smaller than the thickness of the thermistor element, the design of the resistor and the internal electrodes are naturally restricted. Therefore, reduction in the resistance and fine adjustment of the resistance value are difficult.
Furthermore, in an NTC thermistor described in the above-described Japanese Unexamined Utility Model Registration Application Publication No. 6-34201, reduction in the resistance is limited although variations of the resistance value can be reduced. When the size of the gap is reduced for each pair of internal electrodes disposed with a gap therebetween on the same plane, it is possible to decrease the resistance value. However, when the gap is reduced, since a short circuit becomes likely to occur, reduction in the resistance is limited.